Combustion control system



Nov. 17, 1953 G. A. PEPLE, JR

COMBUSTION CONTROL SYSTEM 2 Sheet-Sheet 1 Filed Oct. 17, 1947 INVENTOR GUSTAVE A. PE PL E J R fBtlMuflUV ATTORNEYS Nov. 17, 1953 G. A. PEPLE, JR

COMBUSTION CONTROL SYSTEM 2 Sheets-Sheet 2 Filed Oct. 17, 1947 v INVENTOR GUSTAVE A. PEPL E ATTORNEYS Patented Nov. 17, 1953 COMBUSTION CONTROL SYSTEM Gustave Adolphus Peple, Jr., Richmond, Va.; Bank of Commerce and Trusts, executor of said Peple, deceased Application October 17, 1947, Serial No. 780,551

2 Claims.

This invention relates to method and apparatus for controlling the volume of air delivered to furnaces and has for its object to provide a method and apparatus for delivering air at a predetermined volume rate beneath the grate of a furnace burning solid fuel, regardless of the thickness of the fire on the grate.

The blowers of forced draft furnace installations are usually driven at a constant speed and the volume of air delivered to the duct, assuming an intake opening to the atmosphere of constant size, is proportional to the resistance of flow encountered in the discharge duct. In the ordinary furnace installation with a forced draft air supply the only significant variable in resistance to the air flow through the furnace is the coal bed. A thick coal bed may offer several times the resistance to air flow that is offered by a thin coal bed, particularly an uneven coal bed which may contain holes where there are no coals at all. Unless, therefore, control dampers are provided to modify the duct pressure the volume of air delivered to the furnace will increase rapidly as the fire burns thinner, producing a very uneven rate of fuel consumption resulting in uneven heat generation and a continuous regulating effort on the part of the thermostatic control system.

By my improved system the dampers in the duct are automatically adjusted inversely to the air resistance supplied by the fire bed so that the sum of the resistance offered by the dampers and the fire bed will be maintained substantially constant, with the result that the air delivered by the blower will be in a volume directly proportional to the speed of the blower. If the blower speed is constant, as is usually the case, particularly in domestic installations, the volume of air delivered will be maintained substantially constant to thereby maintain a constant rate of combustion in the furnace.

The invention is primarily useful in connection with coal-burning stoker-fired furnaces having blowers for supplying the combustion air, but the invention may be used with advantage with hand-fired furnaces or in any other situation where it is desired to maintain a constant volume of air output from a duct, notwithstanding variations in the resistance encountered in the discharge flow from the duct.

The principal object of my invention is to provide a method and apparatus of the class described which is entirely self-contained and fully automatic and wherein the power for operating 'the adjustable elements is furnished by the pressure in the duct itself.

A further object of the invention is to provide a method and apparatus of the class described whereinthe air delivery rate may be readily regulated through a wide range.

A further object of the invention is to provide an apparatus of the class described which is of simple, rugged construction, which contains few moving parts, and which can be readily applied to existing furnace installations.

Other objects and advantages of the invention will appear from the following specification and drawing wherein I have illustrated a preferred form of apparatus installed in connection with a forced draft stoker-fired furnace of conventional design.

In the drawings,

Fig. 1 is a side elevation of a typical furnace installation wherein the blower is equipped with my improved volume control regulating mechanism; and

Fig. 2 is a plan view of the mechanism shown in Fig. 1.

Referring to the drawings, I indicates a coalburning furnace of ordinary construction having an ash-pit 2 to which is connected in the usual manner a duct 3 from the forced draft blower 4. Overlying the ash-pit is a grate, not shown, to which the coal is fed by a stoker diagrammatically shown at 6. The stoker 6 and blower 4 are driven in the usual manner from a common electric motor 1 (see Fig. 2) whose operation is usua ly controlled by a thermostatic mechanism, not shown.

The blower illustrated is of the centrifugal type and has its air intake through a cylindrical drum 8 attached to one side wall of the blower in alignment with its axis of rotation. The air from the blower 4 is delivered to the duct 3 and between the blower and the ash-pit of the furnace a damper mechanism is installed in the duct.

I preferably use a damper mechanism such as shown in my prior Patent No. Re. 22,870, consisting of two curved dampers I0 pivoted, respectively, to the top and bottom walls of the duct with their free ends projecting toward the furnace. The dampers are adjusted in synchronism by a linkage H from fully open position illustrated in solid lines in the drawing to the closed position shown in dotted lines, wherein the free edges of the dampers contact each other along the median plane of the duct. With this arrangement of dampers as described in my above mentioned patent, vortex and eddy currents are eliminated and the volume of air delivered under a constant pressure varies directly as the damper opening.

For operating the dampers I preferably provide a bellows l2 mounted on suitable supports I! attached to the upper wall of the duct 3 and enclosed in a removable sheet metal housing l4. The bellows consists of two plates connected by a flexible bag IS in the usual manner. The upper plate I6 is provided with a projecting arm which is connected by means of a link II with the upper damper blade Ill. When the bellows is expanded to the full extent permitted by the link I! the dampers will be fully opened. The bellows is biased to a closed position by a continuous spiral spring ll which encircles the flexible bag It and also by a weight IO attached to the back of the upper damper blade l0.

To expand the bellows and thereby open or partially open the damper, air under pressure is supplied to the bellows from the blower 4. To an; aid the bellows I6 is provided with a pipe 28 which leads from an opening in the bottom plate ii of the bellows to the middle band of a 1' 2i projecting from the side of the blower easing at a point coinciding approximately with the entrance to the duct (see Fig. 2). One end 01 the T 21 connects with an elbow 22 within the duct casing which has its .face opening toward the air stream. The other end or the T is connected by means of suitable fittings to a valve housing 24 supported within a casing 25 which is suspended from the under side of the cylindrical intake drinn 8 of the blower.

The housing 25 is divided into .two chambers by a flexible diaphragm 26 and supported by the diaphragm '26 is a valve '21 co-operating with a valve seat on the valve housing 24. The lower chamber of the housing 25 is open to the atmosphere by means of openings 28 which are 0! sufficient area for the interior of the chamber to remain at atmospheric pressure regardless of variations 'in the volume of air discharged through the valve 21.

The open end of the cylindrical drum 8 is partially closed by means of a diaphragm 30 having a central orifice H for the intake of air.

-'I'he prmsure differential on opposite sides of the diaphragm is directly proportional to the volume of air passing-through the orifice, and the absolute pressure within the housing 8 therefore varies inversely as the volume of air passing through the orifice in the diaphragm. An opening 32 is provided in the bottom wall of the drum 8 to thereby maintain the upper chamber of the housing 25 in communication with the intake side of the blower which, as stated above, is at a sub-atmospheric pressure inversely proportional to the volume of air -delivered to the blower.

The upper chamber of the housing is provided with .a regulating valve 35 by means of which the pressure in the chamber above the diaphragm may be modified. As shown, this valve consists 01' a threaded valve stem 36 which can be screwed down against a valve seat 3! surrounding an opening 38 into the chamber above the diaphragm. The pressure in the chamber can thus be regulated from atmospheric pressure to any degree of sub-atmospheric pressure down'to that existing in the drum 8.

The operation of the device will now be described.

In normal operation the stoker and blower are driven from the same motor to supply dual and air to the furnace. When the space heated from the furnace reaches the desired :maximum temperature the thermostat cuts on the supply of current to the motor, thereby stop ins the stoker feed and blower. when the blower stops the pressure in the duct quickly falls to atmospheric pressure, whereupon the spring IO and weight l9 close the dampers l0 so that the tire will burn very slowly. with the dampers thus shut oil the heat generated by the furnace ialls to a small percentageoi the capacity of the furnace and the space heated by the furnace will (all in temperature to a point where the thermostat closes the switch and supplies current to the driving motor I. As soon as the blower is in operation pressure is built up in the duct I and air under pressure through the elbow 22 and pipe 20 is delivered to the bellows, expanding the bellows and opening, or partially opening, the dampers.

The operation of the blower also produces in the housing 25 above the diaphragm 26 a subatmospheric pressure, which sub-atmospheric pressure is inversely proportional to the vokune of air passing through the intake orifice 31, that is to say, the greater the volume 0! air passing through the orifice 3! the lower the pressure above the diaphragm 26. This subatmospheric pressure on top of the diaphragm 26 will be overbalanced by the atmospheric pressure on the underside of the diaphragm, and the valve 21 will be lifted. thereby permitting air passing into the T 2| through the elbow 22 to escape, thus modifying the pressure in the pipe 20 in accordance with variations in the volume of air delivered by the blower. It the fuel bed thickens the duct pressure will build up, and the volume at air delivered by the :blower will {all oil. The pressure of the air above the diaphragm 26 will then rise and tend to close the valve 21, thus reducing the escape of air through the valve and increasing the pressure in the pipe 20. An increased pressure in the pipe :20 tends to expand the bellows and open the dampers, thus reducing the resistance in the duct with a corresponding increase in the volume 01' air delivered to the furnace.

If the fuel bed thickness decreases or holes develop in the fire, reducing the resistance to the now of air with a consequent reduction in the duct pressure, the volume of air delivered by the fan will increase thereby reducing the pressure above the diaphragm 26 and opening the valve 21 to a greater extent. This will result in a reduced pressure on the pipe '20 and a partial clue ing of the dampers Ill. The dampers III are thus always maintained in a position such that the sum of the resistance oi-the dampers and the resistance of the fuel bed is constant, with the result that the volumeoi air delivered by the fan is constant. By means of the valve the pressure above the diaphragm 28 can be varied to thereby vary the volume oi air delivered at the maintained blower speed. By this means the apparatus .can be adjusted to maintain the proper ratio of iuel'ieed and air flow iorhigh oombustion efiicicncy.

The mechanism is very stable. The dampers are automatically adjusted insynchronism with changing fuel Ebed conditions :without hunting. The apparatus is of simple construction with .few moving parts and is entirely self-eontained, requiring no supplemental power connections orthe like.

applicable to control systems wherein the stake:-

feed is varied in accordance with the demand for heat.

It will be understood that while I have described my improved damper control in connection with a furnace, it is also adapted for use in any situation where it is desired to maintain a constant volume delivery of air irrespective of variations in the resistance to air flow at the discharge end of the duct.

While I have shown and described a preferred embodiment of my invention as designed for use for combustion control, it will be understood that the structure may be variously modified within the scope of the appended claims.

I claim:

1. In a coal-burning furnace, a stoker, a blower, means for driving the stoker and blower at fixed relative speeds, a flue leading from the blower to the furnace beneath the fuel bed thereof, a damper in said flue, an expansible pneumatic chamber connected to said damper for shifting the same in accordance with the pressure of the air in said chamber, a conduit from the pressure side of said blower to said chamber and means operatively associated with said conduit and responsive to variations in the volume of the air delivered by said blower for modifying the pressure in said conduit in accordance with variations in the volume of air delivered by said blower.

2. In a coal-burning furnace, a stoker, a blower, means for driving the stoker and blower at fixed relative speeds, a flue leading from the blower to the furnace beneath the fuel bed thereof, a damper in said flue, an expansible pneumatic chamber connected to said damper for shifting the same in accordance with the pressure of the air in said chamber, a conduit from the pressure side of said blower to said chamber and means operatively associated with said conduit and responsive to variations in the volume of the air delivered by said blower for modifying the pressure in said conduit in accordance with variations in the volume of air delivered by said blower, said means comprising a discharge port in said conduit, a valve for regulating the size of said port, and means for moving said valve in accordance with changes in the pressure at the suction side of said blower.

GUSTAVE ADOLPHUS PEPLE, JR.

References Cited in the file of this patent UNITED STATES PATENTS 

